Um... don't have any tips. I usually stay away from the stage. However, know that you have my support.
Ubi caritas est vera, Deus ibi est.
"The mark of your ignorance is the depth of your belief in injustice and tragedy. What the caterpillar calls the end of the world, the Master calls the butterfly." ~ Richard Bach
Pray that you don't get a sore throat the day of, like I did last year. And bring plenty of water. I don't know what the conditions are like in your theater, but in the one at our school, it's really dry and dusty. I'm shocked I got through the audition...AND made callbacks. This year I hope to actually get in one of our spring musicals (we have two drama clubs and each has a fall play and a spring musical. Last year I could only try out for one of them, and this year my mom thinks I'd be wasting my time trying to get into them. But that's not going to stop me.)
Anyhow, good luck! Er...break a leg! But not literally!
"You do ill if you praise, but worse if you censure, what you do not understand." Leonardo Da Vinci
